Wheel or track slippage, i.e., slip, poses a problem for many work machines, such as tractors. A certain amount of slip may be desired for efficient operation in the field, however excessive slip may cause burrowing into the field or even cause the tractor to become stuck.
To control slip, one technique regulates the position of a plow or other tool pulled by the tractor. The plow is raised when an excessive slip is detected, and lowered if more slip is desired. By raising the plow, the amount of drag or draft of the tractor is reduced, thereby causing a reduction in slip, and by lowering the plow it is increased, thereby typically causing an increase in slip.
While considerable variation exists for conventional control schemes for slip, they typically compare the actual slip of the tractor with the desired slip. In general, an error signal equal to the difference between the two is then used as an input to an actuator which raises the plow when the desired slip is greater than the actual slip and lowers the plow when the reverse is true.
Although this technique works, it suffers stability problems because it only reacts after a particular error condition has been sensed (the slip being greater or less than desired). This technique is not able to predictively modify the characteristics of the control algorithm.